1. Field of the Invention
This invention relates generally to measurement and data acquisition systems and, more particularly, to the improvement of counter functionality in data acquisition systems.
2. Description of the Related Art
Measurement systems are oftentimes used to perform a variety of functions, including measurement of a physical phenomena, measurement of certain characteristics or operating parameters of a unit under test (UUT) or device under test (DUT), testing and analysis of physical phenomena, process monitoring and control, control of mechanical or electrical machinery, data logging, laboratory research, and analytical chemistry, to name a few examples.
A typical contemporary measurement system comprises a computer system, which commonly features a measurement device, or measurement hardware. The measurement device may be a computer-based instrument, a data acquisition device or board, a programmable logic device (PLD), an actuator, or other type of device for acquiring or generating data. The measurement device may be a card or board plugged into one of the I/O slots of the computer system, or a card or board plugged into a chassis, or an external device. For example, in a common measurement system configuration, the measurement hardware is coupled to the computer system through a PCI bus, PXI (PCI extensions for Instrumentation) bus, a GPIB (General-Purpose Interface Bus), a VXI (VME extensions for Instrumentation) bus, a serial port, parallel port, or Ethernet port of the computer system. Optionally, the measurement system includes signal-conditioning devices, which receive field signals and condition the signals to be acquired.
A measurement system may typically include transducers, sensors, or other detecting means for providing “field” electrical signals representing a process, physical phenomena, equipment being monitored or measured, etc. The field signals are provided to the measurement hardware. In addition, a measurement system may also typically include actuators for generating output signals for stimulating a DUT. These measurement systems, which can be generally referred to as data acquisition systems (DAQs), are primarily used for converting a physical phenomenon (such as temperature or pressure) into an electrical signal and measuring the signal in order to extract information. PC-based measurement and DAQs and plug-in boards are used in a wide range of applications in the laboratory, in the field, and on the manufacturing plant floor, among others.
Multifunction DAQ devices typically include digital I/O capabilities in addition to the analog capabilities described above. Digital I/O applications may include monitoring and control applications, video testing, chip verification, and pattern recognition, among others. DAQ devices may include one or more general-purpose, bidirectional digital I/O lines to transmit and receive digital signals to implement one or more digital I/O applications. DAQ devices may also include a Source-Measure Unit (SMU), which may apply a voltage to a DUT and measure the resulting current, or may apply a current to the DUT and measure the resulting voltage.
Typically, in a measurement or data acquisition process, analog signals are received by a digitizer, which may reside in a DAQ device or instrumentation device. The analog signals may be received from a sensor, converted to digital data (possibly after being conditioned) by an Analog-to-Digital Converter (ADC), and transmitted to a computer system for storage and/or analysis. Then, the computer system may generate digital signals that are provided to one or more digital to analog converters (DACs) in the DAQ device. The DACs may convert the digital signal to an output analog signal that is used, e.g., to stimulate a DUT. More often than not, DAQ devices also include counter/timer modules for multiple applications. In counter mode, these modules may count external events, perform time related measurements and interface with several types of position measurement sensors. In timer mode, these modules may generate pulses and pulse trains in several different ways. The pulses generated by the modules may be used to control external devices.
Many DAQ devices incorporate one counter and several logic circuits around the counter to make it perform several different functions. This configuration provides sufficient support for some functions, but there are several common functions that may require more than one counter. An example of such a function, or operation is the generation of a finite pulse train. While one counter is needed to count the pulse specifications (how long the pulse should be kept high, and how long the pulse should be kept low), a second counter may be required to count how many pulses have been generated, and stop the first counter when the operation is complete. Another operation that may require more than one counter is frequency measurement. In this case, a first counter may be used to measure the number of periods of the signal of interest (using a sample clock to define the measurement period), while a second counter may be used to measure precisely the time elapsed for that number of periods. The use of two independent counters, however, limits the range of possible solutions, and further improvements are therefore desirable.
Other corresponding issues related to the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.